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51 Cards in this Set

What is the most aboundant of the four major classes of biological molecules?

- out of proteins, nucleic acids, lipids, and carbohydrates, carbs are the most numerous

Sugars are polyhydroxy ___________ or ___________. Biological sugars are in the _____ configuration, which is determined by ___________________________.

- aldehydes or ketones

- D

- the absolute configuration at its highest numbered asymmetric carbon

Define:
- stereoisomers
- enantiomers
- diastereomers

- stereoisomers: same chemical formula but differ in atomic arrangement
- enantiomers: stereoisomers that are mirror images of each other (have identical chemical and physical properties)
- diastereomers: stereoisomers which are NOT mirror images (different chemical and physical properties)

Most drugs today are resolved. What does this mean, and how is it done?

- resolved means that you have separated out the enantiomers to either D- or L-
- Racemic mixtures can be separated out by derivatizing the mixture with another chiral reagent and then separating the D- and L- forms

What is the Lobry de Bruyn-van Ekenstein reaction?

- C-2 epimerization of sugars occurs under alkaline conditions
- you will get interconversion of an aldose to a ketose if you put a sugar in base

Under physiological conditions, what types of sugars can be oxidized? What about under basic conditions?

- only aldoses (NOT ketoses) can be oxidized (-CHO to -COOH)
- under basic conditions and in the presence of Ag+ or Cu2+, both ketoses and aldoses are oxidized

What are some common mechanisms for oxidizing sugars?

- (-CHO)+Br2 and H20 will give (-COOH)
- dilute HNO3 will create an aldaric acid, where both ends of the sugar now have COOH

What are some common mechanisms for reducing sugars?

- using NaBH4, can get (-CHO) to reduce to an alditol (-CH2OH)

How are hemiacetals formed?

Why is this reaction important?

- an alcohol (ROH) attacks an aldehyde (R-COH) and forms a hemiacetal (R-COH-OR')
- a hemiacetal is a C with two O's attached

- this is how aldose sugars are cyclized

Looking at a Haworth projection formula, how can you tell if a cyclic sugar is in the alpha or beta form?

- alpha: the OH on C1 is on the opposite side of the CH2OH
- beta: the OH on C1 is on the same side as the CH2OH

A sugar with a 6-membered ring is called a ________ while a sugar with a 5-membered ring is called a _________. Two cyclic sugars that differ only in the configuration of the __________ are called __________.

- the C4 alcohol end of the sugar (ROH) attacks the ketone end of the sugar (R'-C-CH2OH) to form the hemiketal
- this results in a 5-C ring

Why does the optical rotation of a freshly prepared solution of D-glucose change?

- due to mutarotation
- a-D-glucose: +112 deg
- B-D-glucose: +19 deg
- The two anomers of D-glucose are diastereomers and have different chemical and physical properties
- this sugar will mutarotate between the alpha and beta configuration to reach an equilibrium of about +52.5 deg for the optical rotation

- each 'hemi' is attacked by another alcohol (R-OH) so that you now have two (-OR) groups attached to the carbon
- GLYCOSIDES: sugar acetals
- can detect them because the C1 carbon is now stable (has an extra R group attached) and will not mutarotate in solution

What two sugars are each of these common disaccharides made from?
- lactose
- sucrose
- maltose
- cellobiose
- isomaltose

- the enzyme B-galactosidase in the small intestine breaks down lactose to galactose and glucose
- as people get older, and if they aren't from a historically dairy-farming region of the world, this enzyme is lost
- lactose can't be broken down, and there is an influx of fluid into the small intestine
- lactose is broken down by the bacteria in the large intestine, causing gas (CO2 and H2)

What is the most abundant biological molecule on Earth?

- cellulose

Why can't humans eat wood?

- wood is made of cellulose
- linear glc-β(1,4)-glc
- human's can't digest this bond
- herbivores and termites have bacteria within their gut that produce cellulases that can degrade cellulose

After cellulose, what is the most abundant biological molecule on earth?

- chitin
- linear β(1,4) polymer of glcNAc

If a patient comes into the ER and has lost a lot of blood, what are they normally given before blood/plasma?

- dextran sulfate IV: causes fluid to come out of tissues and expands blood volume
- is a linear α(1,6) linked glucan that is water soluble
- produced by certain bacteria growing on sucrose

What is starch composed of?

What keeps it from being totally soluble in water?

Where is each portion digested in the body?

- α-amylose: linear α(1,4) glc polymer
- amylopectin: very large branched polymer of α(1,4)glc with α(1,6) branches every 24-30 residues
- amylopectin is insoluble in water

- amylopectin is in small intestine, while amylase is present in salivary secretions